Of increasing commercial value are mercaptan terminated liquid polymers exemplified by the early polysulfide material produced under U.S. Pat. No. 2,466,963. More recent polymers include the mercaptan terminated polyethers of U.S. Pat. No. 3,431,239, and the mercaptan terminated urethane modified polyethers of U.S. Pat. Nos. 3,923,748, 3,446,780, and German Pat. No. 0,066,167. Mercaptan terminated polythioethers are disclosed in U.S. Pat. No. 4,366,307.
The mercaptan terminated polymers are typically supplied as liquid materials which are applied to various surfaces and cured to form solid elastomeric sealants. All of these liquid materials contain small quantities (0.5 to 3 weight percent) of low molecular weight mercaptan compounds which produce undesirable odors that generally limit application of the sealants to well ventilated areas. Attempts have been made to reduce the odors by heating batches of the liquid material under vacuum, with or without the presence of an inert gas. However, the polymers frequently depolymerize, oxidize or otherwise decompose before a low odor product is obtained.
It would be desirable to provide a method for treating the liquid mercaptan terminated polymer materials to reduce the level of odor causing low molecular weight mercaptan compounds in the liquid material without decomposing or otherwise adversely affecting the material.
Most of the presently available single component sealants based upon mercaptan terminated liquid polymers cure from the polymer surface inwards into the body of the polymer at a rate of around 1 mm per day. The cure rate may be increased using various additives, such as catalysts and promoters. Also curing conditions may be controlled in order to increase cure rates. Shortened cure times are desirable since it reduces the amount of time that the applied sealant exists in a tacky, non-solid form. Accordingly, there still is a present need to provide methods for increasing the cure rate of the liquid mercaptan polymers without adversely affecting the quality of the cured elastomer sealant.